1. Field of the Invention
This invention relates to communication switching systems having distributed control and modular design.
2. Description of the Prior Art
Several modular switching systems are known in the prior art. Subdividing systems into complete modules allow stepwise extension or module replacement in case of failure. One of the prior art switching systems has a control which is not centralized, but distributed over the modules. Accordingly, during an operation there is a fixed assignment between each module and a particular area of the system, e.g., a particular group of lines, so that an optimum utilization of the modules is not possible.
Even in prior art modular systems, a central control is mostly provided which in turn is not modular. Under such conditions the advantages of stepwise extension and mutual replacement of modules are not possible for the central part of the system. This is particularly true for program control (computer control) switching systems comprising a central processor. Though these computer control systems are very flexible and allow provision of numerous services otherwise not available, they generally lack the advantages of modular systems. At least, the core of the system must be provided in duplicate if a breakdown of the total system, due to specific failures, is not acceptable. See for example, U.S. Pat. No. 3,856,993, filed Oct. 16, 1973, by Felix H. Closs et al, entitled "Time Division Multiplex Exchange," a continuation of Ser. No. 206,614, Dec. 10, 1971, now abandoned and assigned to the same assignee as the instant application.
Modular data processing systems are known in the art which comprise a plurality of computers. However, in these systems, central control is always assumed by one of the computers. Furthermore, the other computers must be particularly prepared for each task to be executed, i.e., program loading, etc. The central supervision and the preparation of individual computers for each task require additional working steps which can result in a relatively high portion of unproductive operating time in a switching system in which many but relatively short and simple tasks must be executed for a great number of customers.